Introduction: Diffusion tensor imaging (DTI) changes are indicative of white matter tract and axonal changes to neural structures in the brain. Degeneration of ipsilateral limbic system structures has been demonstrated in temporal lobe epilepsy, and reorganization of contralateral limbic system structures has been observed following anterior temporal lobectomy. These post-operative changes in mesial temporal lobe structures have been shown to correlate with continued post-operative seizures and cognitive function. To date, no study has examined the changes seen in white matter structures following laser interstitial therapy for selective amygdalohippocampectomy.
Methods: DTI evaluation was performed in 6 patients (median age, 53; age range, 17-69 years) who underwent pre- and serial post-operative MR imaging as part of routine follow-up after MR laser guided thermal ablation for selective amygdalohippocampectomy for epilepsy. Tensor metrics were obtain in the subacute period (<3 months, 36 days median follow-up) after surgery. We evaluated the following limbic system structures on the side contralateral to the surgical side: hippocampus, amygdala, parahippocampal gyrus.
Results: The most significant changes to the contralateral limbic system white matter structures were an 18 and 16% increase in mean diffusivity (MD) seen in the hippocampus and amygdala, respectively. There was also a 9% increase in the MD of the parahippocampal gyrus. Finally, there was a 16% increase in the fractional anisotropy of the white matter tracts running through the parahippocampal gyrus.
Conclusions: Post-operative diffusion MR imaging following laser interstitial therapy for selective amygdalohippocampectomy demonstrated increased MD in contralateral limbic structures and increased FA in the white matter tracts of the parahippocampal gyrus. These changes are indicative of structural reorganization of contralateral limbic system structures following laser interstitial therapy for selective amygdalohippocampectomy.
Patient Care: We describe changes in white matter structures following laser interstitial therapy for epilepsy. Changes within limbic system structures in epilepsy have been shown to be correlated with clinical outcomes such as seizures frequency and cognitive function. As this procedure gains wider use as a first line modality for epilepsy treatment, it will be important to understand post-procedural changes in white matter structures and the influence they have on clinical outcomes.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Interpret and analyze MRI DTI sequences to assess white matter tracks
2) Describe DTI and white matter changes seen in epilepsy and following epilepsy surgery
3) Understand changes in contralateral limbic system white matter structures following following laser interstitial therapy for selective amygdalohippocampectomy